The addition of dimethoxymethane (DMM or methylal) and diethoxymethane (DEM or ethylal) to a rich ethylene/oxygen/argon flame has been investigated by measuring the depletion of soot precursors. Three rich premixed ethylene/oxygen/argon (with and without added methylal or ethylal) flat flames have been stabilized at low-pressure (50 mbar) on a Spalding-Botha type burner with the same equivalence ratio of 2.50. Identification and monitoring of signal intensity profiles of species within the flames have been carried out by using molecular beam mass spectrometry (M.B.M.S.). The replacement of some C2H4 by C3H8O2 or C5H12O2 is responsible for a decrease of the maximum mole fractions of the detected intermediate species. This phenomenon is noticeable for C-2-C-4 intermediates and becomes more effective for C-5-C-10 species, mainly when C3H8O2 added. A new kinetic model has been elaborated and contains 546 reactions and 107 chemical species in order to simulate the three investigated flames: C2H4/O-2/Ar, C2H4/DMM/O-2/Ar and C2H4/DEM/O-2/Ar. The reaction mechanism well reproduces experimental mole fraction profiles of major and intermediate species, and underlines the effect of methylal and ethylal addition on species concentration profiles for these flames. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.